The development of prostate cancer is due to the loss of tumor suppressor genes and activation of proto-oncogene. Accumulating evidence has implicated the tumor microenvironment in cancer progression and metastasis by secreting of various molecules from immune cells such as cytokines and chemokines. Another molecule that is secreted by tumor microenvironment is reactive oxygen species (ROS), which is associated with tumorigenesis by modulating anti-cancer and pro-cancer pathways. In prostate cancer, the chemokine receptor, CXCR4, is expressed on the cell surface and is associated with cancer cell survival and development. It has been observed that CXCR4 is overexpressed on the cell surface of prostate cancer cells, which directs metastatic cells to tissues where its ligand SDF1[unreadable] is overexpressed. In our preliminary data, we observed an increase of CXCR4 expression in prostate cancer cells treated with ROS. The Phosphate and Tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor which protects cells from becoming cancerous by regulating cell division, repair DNA damage and initiating apoptosis. Loss of PTEN is typically due to genetic deletions, mutations and epigenetic modulations. However, accumulating evidence suggests that PTEN may also be catalytic inactivation by ROS. In a recent study, we have shown that the reconstitution of PTEN in PTEN-null prostate cancer cells inhibited CXCR4-mediated functions;suggesting that loss of PTEN functions as a molecular switch that promotes CXCR4-mediated metastatic events. Additional preliminary studies have shown that ROS increased activated AKT, a pro-cancer signaling pathway in prostate cancer cells treated with ROS. Considering the effects of ROS on both CXCR4 and PTEN, we hypothesis that ROS promote CXCR4-mediated metastasis by regulating PTEN in prostate cancer cells. To accomplish this objective we will: (i) investigate whether ROS inactivates PTEN catalytic activity by performing a cysteine alkylation analysis and phosphatase activity assay;(ii) elucidate the mechanism by which ROS regulates CXCR4 and SDF1[unreadable] expression by flow cytometry and ELISA assay. Furthermore we will determine whether ROS up-regulation of CXCR4 is through the PI3K/AKT/HIF1[unreadable] pathway by western blot analysis and luciferase assay;(iii) determine whether ROS promotes CXCR4-mediated migration, proliferation and invasion by a migration assay, [[3]H] thymidine incorporation assay and invasion assay, respectively. We will also asses the activity of MMP activity to validate cell invasion.